Touch screen controllers (“TSC”) are used in a multitude of commercial products, such as “smart” mobile phones, and can also be found in iPhones® or iPads®. TSC can be used either on resistive touch screens or capacitive touch screens. Capacitive TSCs can generate such information as multi-finger placement on a touch screen. However, capacitive touch screens can also be prohibitively expensive. Therefore, resistive touch screens are sometimes used as a less-expensive alternative.
U.S. Patent Publication No. 2010/0277417 A1 to Sarasmo, entitled “Resistive Touch Screen Apparatus, A Method and a Computer Program” is one example of a prior art multi-touch resistive touch screen.
FIGS. 1Ai-1Aii illustrate the Sarasamo resistive TSC approach. F Referring to FIG. 1Ai, a voltage (“V1”) is measured across an internal reference resistance 120, as a function of a voltage division between a sensor resistor 110 and the internal reference resistance 120. The prior art TSC recognizes that, for a certain reference voltage V1, a “no touch situation” is indicated, as the voltage V1 is measured as being at a given threshold.
In FIG. 1Aii, in an event of a “single touch”, the sensor resistor 110 is bisected or “split” into a first sensor resistor 112 and second sensor resistor 114, and a contact is made at a bottom resistor plate, and the bottom resistor plate is “split” into a first bottom resistor 122 and a second bottom resistor 124. A measurement of voltage V1 is then made over reference resistor 120; this voltage would typically decrease. This decrease in the voltage V1 measured at the reference resistor indicates a “single touch.” An amplitude of the reference voltage position of the “single touch” can be used to determine a position of a “single touch.”
In FIG. 1Aiii, in an event of a “dual touch”, a second part of a resistive screen is touched, represented by a second resistive bisection with a top sensor resistor 132 and 134, and a bottom sensor resistor 142 and 144. This again further lowers a voltage measured across internal sense resistor 120 indicating a “dual touch.” Moreover, the voltage measured at the internal reference voltage 120 can indicates a position and orientation of the “dual touch”.
The above can be better appreciated in FIG. 1B, an illustration of a prior art method 150 for determining finger positioning.
In FIG. 1B, in a step 160, it is determined whether the reference voltage is above a first, higher threshold (“T2”). If it is, in a step 165, it is determined that no touch has occurred, and the method 150 stops.
In a step 170, it is determined whether the voltage is above a second, lower threshold (“T2”). If it is, in a step 175, it is determined that a “single touch” has occurred, and the reference voltage, and the voltages across the first bottom resistor 122 and the second bottom resistor 124 are measured, and the method 150 stops.
Alternatively, in a step 180, it is then determined that a dual touch has occurred, and the reference voltage, and voltages v2 and v3, which are used for distance of the two fingers input and the orientation of the fingers, are measured.
FIG. 1C illustrates various relationships representing dual finger position and orientation.
In FIG. 2A, a current is measured between a Vcc and a ground for a prior art single touch. However, as is illustrated, characteristics of the bottom plate are not measured only a current through the top plate. For purposes of explanation, a single touch does not affect a measured current.
However, in FIG. 2B, two fingers are used, with two different contact positions, and resistor R2 is in series with resistors R3, thereby increasing current, as a parallel current path through R2 in series with R3 in parallel to R1 has been created as used in a prior art dual touch circuit.
FIG. 3A illustrates prior art calculations that can be made regarding location of two fingers.
FIG. 3B illustrates that for a single touch, a current magnitude of “I”, such as through R2, is constant and does not change. For a dual touch, however, current magnitude “I” through R2 is in proportion to a distance between two fingers, but not in proportion to the absolute position of the two fingers.
FIGS. 4A and 4B illustrate a prior art circuit 400 for measuring an x position that combines both a single touch measurement and a dual motion measurement of a dual touch. In the circuit 400, a voltage is measured across a sense resistor, such as Rx2, to determine an x position of a single touch. Please note that if the current through the resistor Rx2 is below a given threshold, the touch is deemed a dual touch, and a different analysis applies. For a single finger, this lowers voltage across resistor Rx2.
In FIGS. 4A and 4B, coordinates of a single touch is measured by divided resisters of X/Y plate. In other words, where there is a single touch, Rx1 and RX2 are divided. These resistances are measured, and a ratio is generated. A distance between two touches is also measured by resistors of X/Y plate, although these resistors themselves change value.
Rx1 and Rx2 represent a flexible top plate that is touchable, and Ry1 and Ry2 represent a bottom plate. Moreover, these Rx and Ry resistors are oriented in a perpendicular orientation.
In other words, when there are two touches, the values of each of the resistances change, as well as the ratios between the resistances (due to perpendicular orientation). The distance between two touches is calculated based on a difference between a no touch resistance and two touch resistance for these values. In FIGS. 4A and 4B, Rc represents the resistance that is created when part of a circuit is shorted, as is illustrated in FIG. 3B.
However, there are certain drawbacks associated with the above prior art. For example, it can be expensive and cumbersome to have additional, external circuitry for the two finger measurement in a resistive prior art TSC, such as Sarasmo.
Therefore, there is a need for an improved approach to dual gesture recognition.